%%
%% The LaTeX Companion, 3ed
%%
%% Example 4-2-15 on page I-306 in "Customization keys for typesetting".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{183.0pt}

%StartShownPreambleCommands
\usepackage{ifthen,color,fancyvrb}
%StopShownPreambleCommands

\begin{document}
\renewcommand\FancyVerbFormatLine[1]
  {\ifthenelse{\isodd{\value{FancyVerbLine}}}%
                     {\color{blue}}{}#1}
\begin{Verbatim}[gobble=2]
  This line should become blue and
   this one will be black. And here
you can observe that gobble removes
not only blanks but any character.
\end{Verbatim}
\end{document}
